Control device



J1me 19419 R. A. WINBORNE ET AL 2,245,345

CONTROL DEVICE Filed Nov. 1, 1959 i y; m 4; g

Inventors: Russell AWinbor ne, Raymond L. Coultrip,

Their Attorney.

Patented June 17, 1941 I UNITED STATES PATENT OFFIQE 2,245,845CONTROLDEVICE Russell A. Winborne, Oak Park, and Raymond L. Coultrip,Waukegan, 111., assignors to Edison General Electric Appliance Company,Inc., Chicago, 111., a corporation of New York Application November 1,1939, Serial No. 302,390

ll Claims.

release switch .of this invention will be described in connection withan electric hot water heater, it is to be understood that it is notintended to limit this invention to such an application since it may beapplied to other types of apparatus and certain features of our new andimproved switch may be applied to control devices in general.

In an electric hot water heater it is customary to provide one or moretemperature responsive devices which operateto maintain the temperatureof the liquid at a predetermined value. With such installations it isadvisable to provide some form of over-temperature release switch whichwill act as a positive safety device to prevent over heating in case offailure of the main control devices. Such an over-temperature safetydevice should be constructed so that it will not automatically recloseat normal ambient temperatures encountered during use but may bemanually reclosed. Furthermore, such a device should be constructed andarranged so that it has a wide operating contact gap so as to lessen thepossibility of flashover, and, in order to insure that the releasetemperature for which the device is set will not change over a longperiod of time, the device must be simpleyet sturdy and must have lowstressed operating members. Other considerations are that the contactsmust break positively and the material selected must stand up over along period of time without corroding.

It is the object of this invention to provide an overtemperature releaseswitch for an electric heater which incorporates all of the aboverequirements so that a sturdy, compact control device is obtained whichmaintains its calibration over a long period of time and which isrelatively simple in construction and may be manufactured at low cost.

It is a further object of this invention to provide a control devicesuitable for an over-temperature release switch so constructed andarranged that when the control is actuated in response to apredetermined high temperature it will remain in the open circuitcondition for all normal ambient temperaturesuntil manually reset.

It is a further object of this invention to provide in anover-temperature release switch an improved construction and arrangementin which, to obtain a positive break of the contacts, the smallmovements of the temperature contact structure is moved only after thetemperature responsive element has accelerated a predetermined amount sothat it imparts a kick to the transmitting means between the element andthe movable contact assembly.

Further objects and advantages of this invention will appear as theaccompanying descrip" tion proceeds and the features of novelty whichcharacterize this invention will be pointed out with particularity inthe claims appended to and forming a part of this specification.

For a more complete understanding of this invention, reference should behad to the accompanying drawing in which Fig. l is an e1e= vation partlyin section of a liquid heater to which the oven-temperature releaseswitch of this invention is applied; Fig. 2 is a top view of the new andimproved control device of this invention; Fig. 3 is a sectional viewtaken on the line 3-3 of Fig. 2 and looking in the direction of the arrows; Fig. i is a plan view partly in section of the control device ofthis invention with the cover and fixed contact structure removed; andFig. 5 is a circuit arrangement showing the electrical connections tothe over-temperature switch when it is applied to a liquid heater havingtwo heater elements and separate temperature responsive control devicesfor each heater element.

Referring to Fig. 1, the control device of this invention has been shownas applied to a liquid heater and in particular a water heater having atank l0 in which'is located a pair of heating elements it and I2, theenergization of which is controlled by a pair of suitable temperatureresponsive devices l3 and I4 mounted on the wall of the tank It. Mountedon the wall of the tank l0 near the top thereof is the over-temperaturerelease switch indicated generally by the numera1 I5. The tank I0 isprovided with suitable inlet and outlet connections [6 and a casing I1is provided around the tank suitable insulating -material l8 beinglocated between the casing and the tank. It is to be understood thatwhile this invention will be discussed with reference to a liquidheater, it has more general application and may be used as anover-temperature release larly to Figs. 3 and 4, it will be observedthat the I control device includes a base plate is made from a good heatconducting material such as brass nickel-plated in order to preventcorrosion.

' Provided near the lower end of the base plate I9 is a bracket 20 madeof a similar material on which is firmly secured one end of atemperature responsive element 2|. The temperature responsive elementcomprises two strips of metal welded together along their lengths andhaving dissimilar thermal coefiicients of expansion. In the particularembodiment of our invention illustrated, the strips of metal comprisestrips of invar and nickel chrome steel. The bimetallic strip 2| issecured to the bracket 20 by means of a plurality of rivets 23. Thecomponent ele- 'ments of the bimetal strip are arranged so that shapedmember 26 is provided with a slot or depression 28 into which isinserted the free end of the bimetal strip 2| which is shaped in theform of a knife-edge 29. The cup-shaped member- 21 is provided with anindentation 30 which is adapted to receive the rounded end 3| of anadjusting screw 32. By means of this latter construction, the resilientmember 24 is adapted to pivot about the end of the adjusting screw.

The adjusting screw 32 is secured in a bracket 33 firmly attached to thebase plate l9 by means of rivets 34 and a lock nut 35 is provided on theadjusting screw 32 for looking it in its adjusted position.

In assembling the elements described thus far, the bimetal element 2| ismounted onits support and the adjusting screw 32 is threaded into thebracket 33. The resilient assembly 24 is then placed between the freeend of the bimetal element and the end of the adjusting screw and byvarying the position of the end 3| of the adjusting screw, the endthrust of the coil spring 25 on the bimetal blade is adjusted.

Arranged adjacent the free end of the bimetal member 2| so as to bemoved in accordance with the snap action movement thereof is a movablecontact structure comprising a block 36 made of some suitable insulatingmaterial ,such as porcelain, on which is mounted a pair of bridgingcontact members 31 which in the preferred form of this invention consistof a layer of precious metal 38 firmly secured to a base metal 39 and towhich a U-shaped bracket 48 is fixed by means of a bolt 4|. In order toobtain a good electrical connection between the bridging contact membersand the fixed contacts with which they are adapted to cooperate, thebridging contact members 31 are loosely mounted on the block 36 by meansof pins 42. As shown in Figs. 3 and 4, the legs of the U-shaped bracket48 extend outwardly from the block 36 and are spaced apart an amountsuflicient to permit the bimetal member 2| to lie therebetween. Providedin each leg of the bracket 40 near the outer edge thereof is a slot 43which is adapted to receive a laterally extending abutment or ear 44integrally formed on each side of the bimetal member adjacent the freeend thereof. By means of the engagement of the abutments 44 with theside walls of the slots 43, snap, action movement of the bimetal memberwill be transy mitted tothe movable contact structure so as to cause itto move in response to the occurrence'ofa predetermined hightemperature.

In order to support the movable contact structure in its operativeposition, there is provided a lever 45 which is pivotally mounted at 46on a bracket 41 secured to the base plate. 59 by means of rivets 48. Thelever 45 is channelshaped over a portion of its length andthe remainderthereof comprises a pair of spaced arms 49 which are adapted to lie onopposite sides of the bracket 48 and to be connected to the legsthereof. In order to insure substantially vertical movement of thecontact structure relative to the base plate [9, a pivotal connection isprovided between the arms of the lever 45 and the legs of the bracket40. In efiecting this pivotal connection, each arm 49 of the lever 45 isprovided with a pin 50 which is adapted to be inserted in an opening 5|located in each leg of the bracket 4'8.

Arranged to cover the elements of the control device, is a housing 52made of some suitable electrically insulating material such asporc'elain. The housing 52 is adapted to lie within the flange |9aprovided on the base plate l9 and is secured to the base plate l9 bymeans of a plurality of screws 53 which are adapted to be threaded intothreaded openings 54 provided in the base plate. Firmly secured to thehousing 52 by means of screws 55 is a plurality of fixed contact members56 which are provided with terminal screws 51 for making electricalconnections therewith. Each of the fixed contact 3 members 56 has weldedthereon remote from the terminal screws 51 contact tips 58 which in thepreferred form of our invention comprise a portion of precious metal,such as silver, secured to a backing portion, such as steel, which maybe secured to the contact members 56 by welding. The bridging contactmembers 31 loosely mounted on the member 36 are adapted to engage thecontacts 58 and to close the circuit controlled thereby.

In order to reduce arcing between the fixed and movable contacts and tomaintain the contacts in engagement until the bimetal element hasaccelerated a sufficient amount to move quickly and with a snap actionunder the influence of the resilient member 24, a coil spring 59 hasbeen provided and the slot 43 provided in each leg of the bracket 40 ismade wider than the width of the bimetallic strip 2|. This constructionpermits the bimetallic member to move a slight amount without causingmovement of the bridging contact carrying block 36 and also permits thebimetal to accelerate under the infiuence of the spring 24 so that akick is imparted to the bracket 40 upon the occurrence of the actuatingtemperature thereby causing a quick, sudden opening of the contacts.

In order to maintain the contact pressure be-' tween the bridgingcontacts and the fixed contacts while such small movements of thebimetal member take place, the coil spring 59 is located 'withintheU-shaped bracket 40 so as to be between the bimetal blade and the member36. The spring 59 is held in position at one end by the headed rivet 68located in the bimetal element and at its opposite end by the head ofthe bolt 4|. This spring member is relatively light in construction butis adapted to exert an upward force on the member 36 so that the movablecontact members 31 are held in engagement with the fixed contacts 58,even though the thrust exerted by the resilient member 24 has beendiminisheddue to slight movement to the left of the bimetal strip 2|.With such a construction, wearing of the, contacts is effectivelydiminished.

As previously stated, control devices suitable for use asover-temperature release switches must be constructed so that thepossibility of flashover is substantially non-existent. This means thatthe gap between the bridging contact members and the fixed contactmembers must be sufliciently wide to reduce the possibility of anelectrical breakdown such as caused by lightning. In addition, anover-temperature release switch must be constructed so that the switchwill. not automatically reclose at any normal ambient temperature. Bothof these conditions are satisfied in the control device of thisinvention by the assembly and initial adjustment of the device. Toillustrate this more fully, the bimetal blade is initially assembled sothat its knife edge moves equal distances above and below the normalswitch center line which is an imaginary line drawn between the roundedend 3| of the adjusting screw and the point of attachment of the bimetalblade. Furthermore, the initial adjustment of the screw 32 is such thatat some predetermined temperature, say 70 F., the switch will remain ineither a closed or an open position and will exert the same forceagainst the fixed contacts 58 as against the stop which is formed by theend of the bracket 40 engaging the base plate l9. By advancing the screw32, the vertical component of the thrust of the spring is increaseduntil sufficient contact pressure is obtained between the fixed andmovable contacts so that a temperature of a predetermined high value,say 200 R, will be necessary to cause the contacts to be opened. Sincethe switch moves equal distances above and below its center line, thedifference of 130 F. between. the initial temperature adjustment and therelease temperature adjustment represents one-half the switch amplitude,the full amplitude being 260 F. With such an adjustment of the switchamplitude, the switch will open the circuit at 200 F. but will notreclose automatically so long as the temperature is above --60 F.Withthe switch moving equal distances above and below the center line, awide operating gap is obtained which substantially removes thepossibility of fiashover-once the contacts are opened.

It is to be observed that with our new and improved control device thetemperature at which the device is adapted to be actuated is controlledby adjusting the position of the screw 32. With such a construction andarrangement, no additional adjusting means are required and once theadjustment has been made, the adjusting screw is locked in position bymeans of the lock nut 35. An opening BI is provided in the end of thecasing 52 to permit access to the screw 32 and a suitable cover 62 isprovided to close this opening.

Since the control device is constructed and arranged so that it will notautomatically reclose at normal ambient temperatures, it is essential toprovide manual means for reclosing the contacts after they have beenopened in response to the occurrence of the predetermined releasetemperature. In accordance with this invention the manual reclosingarrangement includes a reset plunger 83 which is loosely mounted in anopening 64 provided in the cover 52 opposite the .end of the channelportion 65 of the lever 45. The reset plunger is provided with a head 66which is adapted to engage the channel portion 65 of the lever and acoil spring 61 is arranged between the head of the plunger 63 and theshoulder 68 of the opening 64 to bias the plunger outwardly with respectto the cover 52. Upon the occurrence of the release temperature thebimetal element is snapped to the left as viewed in Fig. 3 and the lever45 is pivoted counterclockwise causing the channel portion 65 to moveadjacent the head 66 of the reset plunger i3. To reset the device, it isnecessary only to press the plunger inwardly. The head 66 will engagethe lever and rotate it in a clockwise direction an amount suificient tocause the control to be snapped to the closed position.

It is believed that the operation of our improved control device isapparent from the preceding detailed description. However, in furtherdescribing its operation, reference will be had to Fig. 5 in which theover-temperature control switch of this invention is shown applied inthe control circuit for the two-element water heater shown in Fig. 1.With the exception of the provision of the over-temperature switch, thecontrolj circuit shown in Fig. 5 is substantially the same as thatdescribed and claimed in United States Letters lja tent 1,892,557,granted December 27, 1932 on an application filed by Francis H.McCormick. Briefly, the circuit includes the heater elements II and I2schematically represented. Arranged to control the energization of theheater elements are the temperature responsive members 69 and l0, morefully described in the aforementioned McCormick patent. The controlmember 69 is of the double-throw type and the circuit is such that theheater element 12 will not be energized until the control member 69 hasoperated to deenergize the heater element ll. Suitable leads areprovided for connecting the elements to the fixed contacts of theover-temperature switch which contacts are in turn connected through asuitable line switch H to a suitable source of electricalsupply 12. Inorder to simplify the showing in Fig. 5, only the moving elements of theover-temperature'switch are illustrated but these are given the samereference characters as above.

In operation, with the over-temperature release switch in its circuitclosing position, the line switch H is closed to connect the heaterelements I! and I2 to the electrical supply 12. The heater elements arethen energized in accordance with the position of the control devices 69and 10 as more fully described in the aforementioned McCormick patentand the Water in the heater is brought to and maintained at apredetermined desired temperature. If for any reason either of thecontrol devices69 or 10 should fail to operate causing the heaterelements to heat the water to a temperature which approaches the releasetemperature of the overtemperature switch, the bimetal element 2| ofthis switch will start to deflect to the left as viewed in Figs. 3 and5. Due to the play provided between the bimetal element and the bracket31, this initial movement of the bimetal element does not cause movementof the contact carrying member 36. Since the spring 59 biases thebridging contact carrying member 36 to the right, the contact pressurebetween the fixed and movable contact remains unchanged during thisinitial movement of the bimetal member even though the verticalcomponent of the force exerted by the spring 25 on the end of thebimetal bladedecreases with such movement. As the temperature continuesto increase, the movement of the bimetal is accelerated and when therelease temperature is reached in the heater tank,

the abutments 44 on bimetal member 2| move against the opposite edges ofthe slots 43 and under the influence of the spring 25 cause the bridgingcontacts to be moved abruptly away from the fixed contacts 58, theextent of this movement being limited by the end of the bracketlllcoming into engagement with the surface of the base plate I9. Since thecontacts are held in engagement by the action of spring 59 it isnecessary to press the reclosing button inwardly causing the lever 45 tobe pivoted so that the switch will be snapped to the closed position.Prior to doing this, however, the operator will have examined thetemperature control devices 69 and ID to determine the cause of the overheating which actuated the over-temperature switch.

While we have shown a particular embodiment of our invention, it will beunderstood, of course, that we do not wish to be limited thereto sincemany modifications may be made and we, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In an over-temperature release switch, a bimetallic temperatureresponsive member fixed at one end and having its opposite end free tomove, pivotally mounted resilient means for engaging said free end ofsaid bimetallic member to cause said memberto move quickly and with asnap action, a bridging contact carrying member, a bracket secured tosaid contact carrying member, and means for loosely connecting saidbimetallic member to said bracket so that said bridging contact carryingmember is moved only in response to the snap action movement ofsaidbimetallic member.

2. In an over-temperature release switch, a bimetallic temperatureresponsive member fixed at one end and having its opposite end free tomove, resilient means for causing said bimetallic member to be actuatedbetween two limiting positions quickly and with a snap action, switchmeans, means for transmitting the snap action movement of said bimetalmember to said-switch means, means for adjusting the temperature atwhich said bimetal member is moved with a snap action, said means beingadjusted so that said switch means are moved to the open circuitposition in response to the occurrence of a predetermined hightemperature and are maintained in this open position for all normalambient temperatures, and manual means for causing said bimetal strip tobe moved with a snap action to effect resetting of said switch means.

3. In an over-temperature release switch, a bimetallic temperatureresponsive member fixed at one end and having its opposite end free tomove, resilient means for causing said bimetallic member-to be actuatedbetween two limiting positions quickly and with a snap action, switchmeans, means for transmitting the snap action movement of said bimetalmember to said switch means, means for adjusting the thrust exerted bysaid resilient means on said bimetal strip to control the upper andlower temperatures at whichsaid bimetal is moved with a snap action,said last mentioned means being adjusted so that the range between thetemperature which causes said bimetal strip to move said switch means tothe open circuit position and the temperature which causes said bimetalstrip to move said switch means from the open circuit positionto theclosed position is such that once the switch means have been snapped tothe open position they will not' automatically reclose at normal ambienttemperatures, and manual means for causing said bimetal strip to bemoved with a snap action to effect a manual reclosing of said switchmeans at temperatures above said predetermined low temperature.

4. In a control device, a bimetallic strip fixed at one end and havingits opposite end free to move, pivotally mounted resilient means adaptedto engage said free end of said bimetallic strip to cause said strip tomove with a snap action, switch means comprising a plurality of fixedcontacts and a bridging contact assembly, a bracket secured to saidbridging contact assembly, means for loosely connecting said bimetallicmember to said bracket so that said bridging contact assembly is movedin accordance with only the snap action movement of the bimetal strip tocause said switch means to perform a controlling function, and,resilient means for maintaining said bridging contact assembly againstsaid fixed contacts during initial movement of said bimetal strip priorto its snap action movement which causes said bridging contact assemblyto be moved away from said fixed contacts.

5. In a control device, a bimetallic temperature responsive member fixedat one end and having its opposite end free to move, resilient meansengaging said free end of said bimetallic member to cause said member tobe moved with a snap action, means for adjusting said resilient memberto vary the temperature at which said bimetallic member is actuated, abridging contact carrying member adapted to cooperate with fixedcontacts to perform a controlling function, means including a slottedbracket for loosely connecting said bimetallic member to said bridgingcontact carrying member so that said bridging contact carrying ,memberis moved only in response to snap action movement of said bimetalmember, and resilient means biasing said bridging contact member againstsaid fixed contacts so that the connection between said fixed andmovable contacts is broken only when said bimetal member moves with asnap action.

6. In a control device, a bimetallic strip fixed at one end and havingits opposite end free to move, resilient means engaging said free end ofsaid bimetallic strip to cause said strip to be moved with a snapaction, means for adjusting said resilient means to preselect therelease temperature at which said bimetallic strip is actuated with asnap action, abridging contact carrying member adapted to cooperate withthe fixed contacts to perform a controlling function,

means including a slotted'bracket for loosely bracket to bias saidbridging contact member against said fixed contacts so that theconnection between the contacts i broken only when said bimetal membermoves with a snap action. '7. In an over-temperature switch, a baseplate, means for supporting a bimetallic strip on said base plate sothat it is fixed at one end and free to moveiat the opposite endthereof, resilient means pivotally mounted on said base plate andadapted to engage the free end of said bimetal strip to cause it to bemoved between two limiting positions quickly and with a snap action,means for adjusting said pivotal mounting to control the temperature atwhich said bimetal strip is moved with a snap action, a cover mounted onsaid base plate, stationary contacts mounted on said cover, a bridgingcontact assembly arranged to engage said stationary contacts, a bracketmounted on said bridging contact assembly and loosely connected to saidbimetal strip so that said contact assembly is moved only in accordancewith the snap action movement of said bimetal strip, and separateresilient means lying between said bimetal strip and said contactassembly for biasing said bridging contacts against said fixed contactsso that the contact pressure between said contacts remains unchangeduntil 'said bimetal strip is moved with a snap action.

8. In an over-temperature switch, a base plate, means for supporting abimetallic strip on said base plate so that it is fixed at one end andfree to move at its opposite end, a spring pivotally mounted on saidbase plate and adapted to engage the free end of said bimetal strip tocause it to be moved between two limiting positions quickly and with asnap action, a cover mounted on said base plate, a plurality ofstationary contacts mounted on said cover, a bridging contact carryingmember pivotally mounted on said base plate so as to move substantiallyperpendicular to said base plate, means for transmitting the snap actionmovement of said bimetal member to saidbridging contact carrying member,said switch means to be actuated between a closed and open circuitposition, means for adjusting the temperature at which said bimetalmember is moved with said snap action, said means being adjusted so thatsaid switch means are moved to the open circuit position in response tothe occurrence of a predetermined high temperature and are maintained inthis open circuit position for all normal ambient temperatures, a covermounted on said base plate, and manual means adapted to engage saidpivotally mounted portion of said switch means to reset said switchmeans after it has been moved to said open circuit position, said manualmeans extending through said cover so as to be operable from theexterior thereof.

10. In an overtemperature switch, a base plate, means for supporting abimetallic strip on said base plate so that it is fixed at one end andfree to move at its opposite end, switch means having a portionpivotally supported on said base plate, means for transmitting movementof said bimetallic member to said switch means to cause said switchmeans to be actuated between a closed and an open circuit position inaccordance with temperature changes, means for effecting movement ofsaid switch means with a snap action, means for adjusting thetemperature at which said switch means is moved from one circuitcontrolling position to the other, said means being adjusted so thatsaid switch means are moved to the open circuit position in response tothe occurrence of a predemeans comprising a bracket mounted on saidbridging contact carrying member and having a pair of slots adjacent theends of the legs thereof and a pair of 'abutments on said bimetal memberarranged to engage the edges of said slots, said slots having a widthgreater than the thickness of said bimetal so that said bimetal may;

be moved a small amount prior to its snap action movement withoutcausing movement of said contact carrying member, and resilient meansengaging said bimetal member and said bracket and adapted to bias saidcontact carrying member against said fixed contact so that the contactpressure between these contacts is unaffected by small movements of saidbimetalj member relative to said contact carrying member.

9. In an overtemperature switch, a base plate, means for supporting abimetallic strip on said base plate so that it is fixed at one end andfree to move at its opposite end, a spring pivotally fixed contacts onsaid cover, bridging contact means adapted to cooperate with saidfixedcontacts to perform a circuit controlling function,

an arm secured to said bridging contact means, means for pivotallymounting said arm within said casing, temperature responsive meansadapted .to engage said arm to cause pivotal ovement thereof andactuation of said bridg-v ing contact means between a closed and opencircuit position in accordance with temperature changes, resilient meansfor effecting movement of said bridging contact means quickly and with asnap act ion, means for adjusting the temperature at which said contactmeans is moved from one circuit controlling position to the other bysaid temperature responsive means, said means being adjusted so thatsaid switch means are moved to the open circuit position in response tothe occurrence of a predetermined high temperature and are maintained insaid open circuit position for all normal ambient temperatures, andmanual means operable to reset said switch means after it has been movedto said open circuit position, said means being actuated from outsidesaid casing.

RUSSELL A, WINZBORNE.

RAYMOND L. COULTRIP.

